Two recently solved x-ray crystal structures of HIV-1 gp120 complexed with CD4 and the Fab fragment of a human neutralizing antibody 17b provided structural details of the interactions between CD4 and gp120 and revealed the presence of a large hydrophobic cavity in gp120 where Phe43 of CD4 binds (Phe43 cavity). The objective of this project is to use a structure-based approach to identify small molecular lead compounds that will bind to this cavity to block the CD4-gp120 interaction and prevent HIV-1 entry to host cells. The specific aims of this proposal are as follows: (1) To identify, by virtual screening of large databases, small molecules that dock into the CD4 binding cavity (Phe43 cavity) in gp120. The automated molecular docking technique will be used as a virtual screening tool to select only those compounds that fit into the cavity and interact with the CD4 binding site in gp120. (2) To identify, by immunological and virological screening assays, lead HIV-1 entry inhibitors that block gp120 binding to CD4. The potential lead compounds will be selected by a two-step process for further studies: (a) the selected compounds from virtual screening will be assayed by high throughput enzyme-linked immunosorbent assays (ELISA) to identify inhibitors that bind to gp120 and block gp120 binding to CD4, and (b) the selected inhibitors from (a) will be further screened for inhibitory activity against HIV-1 mediated cell fusion and cytopathic effects (CPE), and for in vitro cytotoxicity. (3) To optimize lead compounds for generating potent anti-HIV-1 agents. The best lead compounds will be optimized further through design of focused libraries and structure-activity analysis (SAR). Overall, this project will yield new lead compounds acting as potential HIV-1 entry inhibitors. The long-term goal of this proposal is to optimize the lead compounds through chemical synthesis and structure activity analyses and select 3-4 best compounds for further preclinical studies as novel ianti-HIV-1 chemotherapeutic agents.